[Prophylactic effect of TLR5 agonist flagellin on acute graft versus host disease after allogeneic hematopoietic stem cell transplantation and its mechanism].

This study was aimed to investigate the prophylactic effect of Toll like receptor (TLR)5 agonist flagellin on acute graft versus host disease (aGVHD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) and its possible mechanism. The animal model with allo-HSCT aGVHD was established by using purebred mice (male mouse C57BL/6 as donor, female mouse BALB/c as recipient) with complete-unidentical major histocompatibility antigen. The recipient mice were randomly divided into 3 groups: group 1 in which mice were injected with high purity (95%) flagellin before and after allo-HSCT respectively, group 2 in which mice received allo-HSCT without injection of flagellin, group 3 in which mice were radiated alone. The aGVHD features of mice in group 1 and 2 were observed and compared. The results showed that the typical symptoms of aGVHD appeared in transplanted mice. The death peak of mice in group 2 appeared at day 4-5 after transplantation. The aGVHD symptoms were obviously alleviated and the mean survival time was prolonged significantly in mice group 1 as compared with mice in group 2 (P < 0.05). The comparison of WBC count in peripheral blood of mice in 3 groups before transplantation showed no significant difference (P > 0.05), while WBC count of mice in group 1 and 2 showed the significant difference at days 14 and 21 after transplantation (P < 0.05). The pathological appearances of aGVHD in mice of group 1 were obviously reduced as compared with mice in group 2. The flow cytometric detection of Treg cell/CD4(+) T cell levels at different time before and after transplantation demonstrated that the Treg cell level in mice of group 1 at weeks 2-4 after transplantation significantly increased as compared with mice in group 2 (P < 0.05). It is concluded that flagellin can effectively prevent the aGVHD occurrence after allo-HSCT, reduce the symptoms and pathological changes of aGVHD, obviously prolong mean survival time of mice in group 1. The mechanism of flagellin effect may be associated to increase of Treg cell level in mice after allo-HSCT.